There is well known a control apparatus for a vehicle provided with a drive power source, and a step-variable transmission which constitutes a part of a power transmitting path between the drive power source and drive wheels and which is placed in a selected one of a plurality of gear or speed positions with an engagement of a selected one or ones of a plurality of coupling devices. A hybrid vehicle disclosed in JP-2014-223888A is an example of this type of vehicle. This document discloses a control apparatus configured to execute a feedback control to control an input torque (e.g., a torque of a second motor/generator in this document) that is inputted to the step-variable transmission, such that a value (i.e., an angular acceleration value of a second motor/generator in this document) representing a state of a rotary motion of an input rotary member of the step-variable transmission coincides with a target value. This document discloses that a limit of the target value of the angular acceleration value of the second motor/generator is changed depending on a degree of progress of the shifting action of the step-variable transmission.
By the way, the degree of progress of the shifting action (hereinafter referred to as “shifting progress degree”) of the step-variable transmission represents a degree to which the shifting action has progressed, and can be determined, for example, based on a rotating speed of the input rotary member of the step-variable transmission which is changed with the progress of the shifting action and a synchronizing speed of the input rotary member which is calculated from a rotating speed of an output rotary member of the step-variable transmission. Thus, if the drive wheels are slipped during the shifting action (particularly, during an inertia phase), a relationship between the rotating speed and the synchronizing speed of the input rotary member is collapsed whereby the shifting progress degree becomes indefinite. Therefore, where the target value of the value representing the state of the rotary motion of the input rotary member is set depending on the shifting progress degree of the step-variable transmission, there is a risk of delay in the shifting action of the step-variable transmission because the slipping of the drive wheels could make it impossible to appropriately control the input torque to the transmission.